Dear Antonio Gutierrez, I noticed that you deleted my solution in Russian to this problem. Will it be acceptable in the futureif I post side by side English-Russian translations of my solutions so that Russian readers can understand them?

Per the problem statement , P is any point on circle center D, radius DC. It may exist a particular point P so that C, O and B1 are collinear, but in general these 3 points are not collinear and angle A1 in triangle A1B1C is not equal 90 degrees. please provide explanation.